Recent advances in surgery Conducted by ALFRED BLALOCK, M.D. The blind-loop syndrome after gastric operations ince the earliest reports by Whitees time, several examples of the blind-loop ANATOMIC CONFIGURATION OF BLIND LOOPS Various examples of gastrointestinal blind and Wangensteen;O a side-arm loop has been employed as in Fig. 1, A, in which the loop is arranged so as to be self-filling. The side loop arrangement is the one which most 849 850 Recent advances in surgery Surgery ;.$ Nouernbcr 1961 & ad cumulated from observations on lesions at differing sites in the gastrointestinal tract. The principles involved apply, with varia- tions, to blind loops at all levels. The best- known feature of the blind-loop syndrome is megaloblastic anemia, which is due to dis- ruption of vitamin BI2 absorption. Normally, dietary vitamin B12 (Castle's extrinsic fac- tor) is absorbed after an incompletely under- stood interaction with intrinsic factor (Fig. 3, A), a mucoprotein secreted by the gastric rnu~osa.*~In man, the principal site of B,, absorption is the ileum.7* Vitamin B,, deficiency can develop by a number of alternative mechanisms. Rarely loops which have caGsed the blind-loop- syndrome.- is there dietary deficiency of this nutritional A, Anastomosis with formation of a self-filled stagnant loop, B, with jejunal diverticulosis, C, factor. Commonly, as in pernicious anemia with intestinal strictures, D, after enteroenteros- (Fig. 3, B) or after total gastrectomy,Sgthere tomies or fistulas, and E, after gastric operation. is absent intrinsic factor due to gastric atrophy or the absence. of the stomach, re- resembles a blind loop which develops after spectively. Malabsorption can also occur4*25* gastrojejino~tom~(Fig. 1, E) . The structural conditions necessary for the blind-loop syndrome are not present after the Billroth I anastomosis. In all re- ported cases there has been either a Billroth I1 resection (8 patients) or a gastroenteros- Pi- ..?* .. tomy (1 patient). The anastomoses (Fig. 2, -5.'. ?: A and 3) were both antiperistaltic, with . the afferent loop to the greater curva- t~re,~~'45 and isoperistalti~.~~~45 In 2 cases (Fig. 2, C and D), an enterostomy had also been performed.'. 49 Commonly, the afferent loop was excessively long and dilated.2" 30* 45 The exact site of obstruction was sometimes difficult to define by roentgenogram or even at operation.l3~459 4B U sually, the distended loop ended abruptly at the gastrojejunos- tomy, but in some cases it extended beyond this. Excessively long afferent loops, kinking at the site of anastomosis, and partially ob- structing adhesions have all been described as the factor causing blind-loop stasis.'. 13* 25, 30. 45, 49 ABNORMALITIES IN VITAMIN B,, METABOLISM IN BLOOD-LOOP *-& SYNDROME Fig. 2. Anatomic conditions after gastric opera- -q tion which have caused blind-loop syndrome. A. ?:. General information concerning the mech- 1 3 CM, B, 3 cases, C, 1 cue, D; 1 case, and E, anism of the blind-loop syndrome has ac- 1 case. ;*&% i Starzl, Butz, and Hartman: Blind-loop syndrome 851 absent absorption Fig. 3. Mechanisms of Bu utilization in normal and diseased patignts. f 2'- 20, 27, ?8, 35, 40, 43, 52, 54 , r with adequate intrinsic drome can proceed to subacute combined ' factor and dietary vitamin BIZ in patients degeneration of the spinal cord.'* s*20* "% who have undergone ileal resection (Fig. 3, Virtually all authorities agree that a t. ,: D) or who have diffuse small bowel disease change in the bacterial flora of the torpid 1' ! (Fig. 3, C). Here, the malabsorption is due imp is responsible for the B,, malabsorption. I 6: to damage or removal of the normal site of Much of the evidence is based upon clinical - absorption. Vitamin BIZ deficiency also de- impression, but there is solid experimental - the presence of intrinsic factor and dietary employing strictures to study the blind-loop ( :, BIZ (Fig. 3, F). The malabsorption in this effect in dogs, related the presence or ab- '", circumstance is thought to be due to bac- sence of infection above the stenosis to the terial overgrowth in n poorly emptying blind development or absence of anemia. Watson #' ' :%. -L- . d.2 v' ,or,, 60 ,or,, . Fig. 4. Various hypotheses to explain malabsorption of vitamin Bu. growth in the small bowel distal to the blind min. The application of these disclosures to loop was changed with a reduction in Lacto- the diagnosis and treatment of the blind-loop bacilli and increases in Esche~ichiacoli and syndrome will be discussed subsequently. alpha hemolytic streptococci. Perhaps the Despite the generous support accorded the most conclusive evidence for the bacterial bacterial theory, the precise mechanism of etiology of the malabsorption was provided vitamin B12 malabsorption is not known. One by Toon and \Yangen~teen,~Oand later con- widely accepted theory is that propounded firmed by \lratson and Witt~.~Theseauthors by M'itts6@in which B,, metabolism is sup- showed that the anemia of the experimental posedly affected by direct alimentary con- blind loop syndrome could be prevented by tamination of bacteria or their toxic by- oral administration of chlortetracycline. The products which spill out of the stagnant loop therapeutic value of antibiotics in man has (Fig. 4, A). Since certain strains of Escheri- been confirmed by Siruala and Kaipainensa chia coli and Streptococcus fecalis metabo- and numerous other observers,', 3. 17, 259 26* 2F, lize folic acid or vitamin BIZ,"* s1 it has been 309 34. 437 49, 50, 54 who noted that certain suggested that the anomalously located mi- antibiotics could not only prevent the de- croorganisms use up the available oral sup- velopment of, but also reverse, B12 deficiency ply. Contrary to this reasoning is the fact by restoring normal absorption of this vita- that Neomycin and sulphonamides, which Starzl, Butz, and Hartman: Blind-loop syndrome 853 are nonabsorbable and which sterilize the OTHER NUTRITIONAL nonstagnant intestine are of no therapeutic DEFICIENCIES IN BLIND- LOOP SYNDROME value'7* 25* 28 despite the fact that they would be expected to come into contact with efflux Absorption of other nutritional substances from the loop. In contrast, oral antibiotics is often impaired. Fat is probably the most such as chlortetracycline, oxytetracycline, commonlg affected. Using experimental mid- and tetracycline can restore normal absorp- intestinal loops, Aitken and colleagues2 found tion of B,,. that virtually all rats exhibited steatorrhea However, if the offending agent were a whether or not the animals became anemic. toxin, its production in a sequestered loop The development of anemia alone, without would be suspended only with a systemic steatorrhea, was uncommon. antibiotic. Drexler18 has shown on the basis As with vitamin B12 deficiency, it is of in vitro experiments that indole com- thought that bacterial overgrowth in the pounds are able to inhibit normal utilization blind loop is the causative factor in the of vitamin B12, and he has suggested that steatorrhea. Specific evidence has been pre- indole might be one of the blind-loop "tox- sented by Sammonssl and by Goldstein and ins." Recently, Hoffman and Spiro30 have his group25 that the bacterial growth ad- failed to support either the bacterial or toxin versely affects fat utilization. The latter theory of direct intestinal contamination. authors have shown that the steatorrhea of They instilled into a normal patient's stom- the blind-loop syndrome is favorably influ- ach the contents of a resected blind loop enced by antibiotics. with Coeo-taggedvitamin BIZ.B12 absorption Why some blind loops do and others do was not depressed. not cause steatorrhea is not known. There is Other theories to explain the B12 deficiency some evidence that the location of the blind involve blood-stream mechanisms. Ungleys2 loop is influential in this respect. BoothT has suggested that a toxin was absorbed from the pointed out that a blind loop of the ileum, blind loop which destroyed the vitamin in where normal vitamin B12 absorption occurs, the blood and tissues (Fig. 4, B). He sup- may lead to pure B12 deficiency. Blind loops ported this opinion by the demonstration of the jejunum, where fat is normally ab- that plasma added from a resected blind sorbed,'. s* 259 33 usually produce prominent loop suspended megaloblastic maturation in teato or rhea.^* 54* 83 While such localization is bone marrow culture. Cardla also proposed admittedly crude, it may help to explain dif- that B,, was actually absorbed, but that in- ferences in the malabsorption defect in dif- crements were returned by enteric recircula- ferent cases. Of 9 $atients who had blind- tion (Fig. 4, C) to the blind loop and de- loop syndromes after gastric operations, 7 he stroyed. Both theories were weakened by the had steatorrhea. of results of studies of urkary and fecal excre- Other nutritional deficiencies are also com- ne tion of radioactive vitamin B12 which show mon. Numerous cases of protein deficiency ed that the block in metabolism is primarily at, have been noted with blind loops at various ! p- rather than after, the absorption phase.,' 3t 17* levels, including the blind loops after gastric m- 25, 28, 28, SO, 34, 40, 43, 45, 49. 50, 54 operation^.^" 259 45 Usually this is reflected in 'Y- ~1.'. An unexplored possibility is that bacterial low plasma protein levels, but 1 example of OP : toxins are picked up from the blind loop frank kwashiorkor has been reported in a ri- '"- and circulated to the uninvolved portion of patient with an intestinal blind loop.38 Pel- m- - the small bowel where they alter the absorp- lagra and vitamin C and vitamin K de- en . - tive capacity (Fig. 4, D). Such a hypothesis ficiencies have been recorded. Badenach3 has xi- is compatible with the evidence obtained warned against the dangerous complication :p- - from antibiotic therapy, and with present of spontaneous retroperitoneal hemorrhage Kt knowledge of the fundamental defect in BIZ resulting from vitamin K deficiency.